Morgan's Canon, also known as Lloyd Morgan's Canon, Morgan's Canon of Interpretation or the principle of parsimony, was coined by 19th-century British psychologist C. Lloyd Morgan,[1] and remains a fundamental precept of comparative (animal) psychology. In its developed form it states that:[2]

In no case is an animal activity to be interpreted in terms of higher psychological processes if it can be fairly interpreted in terms of processes which stand lower in the scale of psychological evolution and development.

In other words, Morgan believed that anthropomorphic approaches to animal behavior were fallacious, and that people should only consider behaviour as, for example, rational, purposive or affectionate, if there is no other explanation in terms of the behaviours of more primitive life-forms to which we do not attribute those faculties.

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Morgan was reacting to interpretations of animal behavior–specifically the anecdotal approach of George Romanes–that he deemed excessively anthropomorphic. The prestige of Lloyd Morgan's canon partly derives from cases he described where behaviour that might at first seem to involve higher mental processes could in fact be explained by simple trial-and-error learning (what we would now call operant conditioning). A famous example is the skilful way in which Morgan's terrier Tony opened the garden gate, easily taken by someone seeing the final behaviour as an insightful act; Lloyd Morgan, however, had watched and recorded the series of approximations by which the dog had gradually learned the response, and could demonstrate that no insight was required to explain it.